The present invention relates generally to wireless communications systems, and more specifically to a high performance wireless broadband communications system that provides increased spectral efficiency in point-to-point and point-to-multipoint applications.
U.S. patent application Ser. No. 11/115,943 filed Apr. 27, 2005 entitled MULTIPLE INPUT MULTIPLE OUTPUT (MIMO) WIRELESS COMMUNICATIONS SYSTEM (the “'943 application”) and assigned to the same assignee of the present invention discloses a wireless broadband communications system that can be configured as a line-of-sight (LOS) or a non-line-of-sight (NLOS) wireless communications system. As disclosed in the '943 application, the LOS and NLOS configurations of the wireless communications system can be deployed in both point-to-point and point-to-multipoint applications, in which at least one transmitter disposed at one end of a communications link transmits data signals over one or more communications channels using specified space-time coding and modulation techniques, and at least one receiver disposed at the other end of the link captures the transmitted data signals and employs specified signal processing techniques to decode and demodulate the signals to recover the user data. The LOS and NLOS system configurations disclosed in the '943 application may employ adaptive modulation techniques to adjust various transmission parameters such as the coding rate and the modulation mode to compensate for changes in channel characteristics that can adversely affect the quality and the rate of the data transmission.
One problem facing wireless broadband communications systems like those disclosed in the '943 application is the ever increasing demand for higher data transmission rates, which is driven in large part by increasing demands for multi-media data services involving, e.g., text, graphics, video, animation, and/or sound. This problem is exacerbated by a number of aspects of the environments in which wireless communications systems are currently being deployed, such as the limited bandwidth capacity of the communications channels available for use by the systems.
For example, in a conventional wireless broadband communications system, data corresponding to a single communications session is typically transmitted from at least one transmitter to at least one receiver over one or more communications channels, each of which is generally defined within a limited portion of the electromagnetic spectrum allocated to the system. To achieve more efficient use of the allocated spectrum, digital communications techniques have been employed in such systems to allow data packets corresponding to multiple communications sessions to be transmitted over one or more shared channels, obviating the need to dedicate one or more channels for each communications session. Such digital communications techniques are commonly employed in wireless communications networks including one or more wireless LANs (WLANs), which typically utilize data packet protocols to communicate between the various nodes of the WLAN. Wireless communications systems may also be configured to operate in shared frequency bands such as the unlicensed frequency band for WLANs located at 5 GHz.
Conventional wireless broadband communications systems employing shared communications channels and shared frequency bands have drawbacks, however, in that they have generally been incapable of providing data transmission rates that are appropriate for all multi-media data services. For example, with respect to wireless communications systems operating in the shared frequency band for WLANs located at 5 GHz, more than one WLAN operating in the shared 5 GHz band may be deployed within the same geographical area due to the unlicensed nature of the 5 GHz band. In addition, radar and other types of wireless communications systems, either operating in the shared 5 GHz band or generating frequency harmonics having components in the 5 GHz band, may also be deployed within the same geographical area. As a result, the communications channels available to such wireless communications systems deployed within a particular geographical area may have increased levels of noise and interference, which can hinder the systems' ability to maintain the desired high rates of data transmission.
It would therefore be desirable to have an improved wireless broadband communications system that provides higher performance and increased spectral efficiency in point-to-point and point-to-multipoint applications. Such a high performance wireless broadband communications system would allow increased rates of data transmission in both LOS and NLOS environments, while avoiding the drawbacks of the above-described conventional wireless communications systems.